How can I set the maximum draw type for multiple objects?
Just right click on the "maximum draw type" list and choose the "copy to selected" option:



Note: this function is available in many contexts (not all).

Additional information:

As said Duarte Farrajota Ramos in the comments, you can use the Alt key whilst clicking on/choosing the wanted 'maximum draw type'. And that will apply it to all selected objects without using the menu indicated above.

But this Alt key won't work here if you have the 'Emulate 3 Buttons Mouse' in the user preferences (which allows to use the alt key to replace the middle button features, if you are using a track pad for instance).